Foundry core



Patented Dec. 18, 1934 UNITED STATES FOUNDRY CORE Edward Weather-ford. Decatur, Ill., aulgnor to The Borden Company, New York, N. 1., a corporation of New Jersey No Drawing. Application November Serial N0. 697,151

8 Claims. (01. 22-188) and inserted'in the molds in such positions that the molten metal flows around them to leave (when the cores are removed) the desired recesses and cavities in the castings. Such cores, commonly termed foundry sand cores or simply foundry cores, are customarily made from a mixture of finely divided inert materialordinarily sandwater, and binder; and are used but once. The ingredients are mixed in some suitable manner, usually by commingling in an edge-runner mill or other mechanical mixing device, so as to coat the inert particles with I the binding material.

The mixture is packed into core molds, more commonly termed "core boxes, which generally are so constructed that each contains one longitudinal half, or other appropriate portion, of the desired core. The completely formed core, which must have the exact configuration of the cavity to be formed, if not molded in one piece, is obtained by bringing together these boxes with their packed-in material, so that the core portions come together to constitute a whole, and then removing the boxes' to leave naked the so-completed green" core. The mix must be of such a consistency as to possess suflicient strength, called green bond strength, to cause the green core thus prepared to maintain its shape.

The completely formed core is next subjected to baking in a core oven at a temperature usually not exceeding 400 F. and for a period of time usually not exceeding two hours. During this baking, the moisture is evaporated and the binder becomes effective, by virtue of its power to hold together the individual sand grains. The core when baked and cooled is a porous object, and yet it possesses considerable strength and hardness.

When the cores are built of separately formed parts, as indicated above, the binder may sufilce to hold the parts of the newly formed core together, so that when the boxes are stripped away the built-up core may be transferred to the baking oven, and there at the same time with the hardening the integration of the builttogether parts may be effected. In particular cases, however, because either of the intricacy of shape of the cores or because of their size, they may not be so brought together and effectively united, and in such cases the core parts will be separately baked, and after baking the then hardened parts will be brought together and secured together to form the integrated core by means of adhesive spread upon the meeting surfaces.

When in the course of the preparation of cores a surface of superior smoothness is desired, it is common practice to coat the surfaces of the baked core with a wash of silica flour, graphite, or other finely divided inert material, and in this preparation a siccative is commonly included.

The art of making cores involves considerable skill in the application of scientific principles. Much thought has been given to the choice of material for the binder. The most commonly used binder materials are of either the oil 'or the dry type. The oil binders are prepared with linseed or other drying oil as the base. The dry binders in commercial use are usually some form of dextrine or dextrose, commonly known in the foundry as corn flour. Many other organic materials'have been proposed for use as core binders, including rosin, sulphite pulp waste liquor, synthetic resins, casein, etc. A

None of the core binders now in practical use possesses all the desirable qualities that are sought for by practical ioundrymen. For example, the cost of the binder is in some cases too great for economical operation. In some cases the strength of the resulting, core is not sufficiently high to permit its application in many types of castings. Frequently, the time required for properly baking the core, prior to its use in the casting operation, is unduly long. A core that has great strength may be exceedingly dimcult to remove, after the casting has cooled. Furthermore, in most cases it is not possible to use again the sand employed in making the core, which results in waste. Many types of binders, particularly oil binders, are objectionable in that, usually containing 1 or 2% of oil, they generate obnoxious gas, both during the period of baking and during the period when used in the mold, upon the introduction of the molten metal.

My invention eliminates such difllculties, and for the first time makes possible the production of a core. using a. relatively inexpensive binder,

which possesses the following combined advantages: high strength, particularly on the surface of the core; short baking time; ease of removal after the casting has cooled; the core sand is left in such condition that to a great extent it can be used again; gas evolution during baking is reduced to a minimum; and gas evolution during pouring of the casting is less objectionable than with other types of binders.

The invention lies in the discovery of the value of milk as a binder material for cores. Specific phenomena occur and superior results are attained. And within the meaning of the term milk I include milk derivatives generally, in which the serum component (whey component) is retained, and (as ordinarily'and advantageously will be the case) other components as well. Specifically, I include skim milk, powdered milk (whole or skimmed), condensed milk (whole or skimmed), evaporated milk (whole or skimmed), buttermilk (fluid or powdered), and whey (fluid or powdered).

In this connection I have determined that, while ordinarily it will be economical to remove and use elsewhere the butter fat, this is not necessary to the efficacy of the binder. This equally applies to the caseinogen content of the raw milk, which is not as soluble and hence not as inclined to migrate as are other components of the milk, and which is in no sense essential to the successful practice of my invention. I have also found that the' natural water content of raw and skim milk may be employed with advantage in particular cases where great core strength is not required. Ordinarly, however, some degreeof concentration will be found desirable, and this, in the usual case, may amount to the removal of at least 25% of the water content.

It has been found in extensive tests, conducted both in the laboratory and in the foundry, that, as a practical matter, powdered skim milk of the usual commercial grade possesses in high degree the desired characteristics; and powdered skim milk is such in form as to be more readily serviceable, and in use more economical, than any other milk derivative. Skim milk powder, therefore, will hereafter be used as illustrative. All such milk derivatives; however, as have been specified above have excellent binding qualities and certain special properties not possessed by any binder used heretofore. In any case, the finely divided inert core material is mixed with the milk or milk derivatives, with water if need be, and the mixture is shaped and dried and, ordinarily, baked in the usual manner.

Because of the relatively high solubility of skim-milk solids, skim milk will act in a way that the usual dry binder will not, or in a manner superior to that of the usual dry binder. When a core has been formed and is undergoing the baking operation, there is migration within it of water from the deeper portions to the surface; and skim milk, if it be employed as the binder (being, at the time of mixing, uniformly distributed throughout the unbaked core), will migrate with the water toward the surface, as (or to a degree that) the usual dry binder will not. In consequence, the binder will be concentrated toward the surface, and will there afford the desired hardness and smoothness. Indeed, in hardness and smoothness of surface, such cores are superior to any heretofore made, be-

cause of the caramelization at the surface of the carbohydrate content of the binder. If

proper amounts of binder and of water have. been used, the centre -of the core will be left relatively free of binder and friable.

sand, and 60 parts of water. On the other hand, it is possible, by increasing the amount of skim-milk powder used and by varying the amount of water and the conditions under which the core is baked, to obtain cores which are hard throughout, and at the same time to maintain a proportionate surface effect of greater strength, as above described.

In order to combine to better advantage for special purposes the binding properties of the various milk solids, I may mix in various proportions the various suitable milk products. Thus, I may combine skim-milk powder with fluid or evaporated or condensed milk; or I may combine powdered skim milk or buttermilk with powdered whey; or effect other combinations, as

desired, to emphasize either the migratory or the flxed characteristics of the several solids.

I have found that my binder as herein described is useful for pasting together the parts of cores that after baking are to be assembled into one whole. Also, when cores are to be coated with a wash of silica, graphite, or other such material, milk powder or other form of milk contemplated may be'added as the siccative in the composition of the wash and the wash may be applied in the usual manner. The milk component then serves both as a dispersing agent in the composition, and as an adhesiv when the wash has been applied.

It will be perceived from what has gone before that there are two qualities or characteristics of the material that I employ, developed in the preparation of the core, that contribute to the integrity and serviceability of the core. One of these is the adhesive eflect, uniting the particles of sand, a phenomenon that manifests itself throughout all the thickness of the corethough, in consequence of baking, of greater strength near the surface. The other quality or characteristic is the hard-shell effect, due chiefly to caramelization. The material is chemically changed by heat-though not oxidized-and the article becomes case-hardened and so better fitted for service.

An important advantage of my binder over an oil binder lies in the fact that it exerts its binding power as soon as the water has been evaporated in the baking, and the attendant process of caramelization has occurred; whereas in the case of an oil binder there must be an oxidation, an aging. before the binder attains its maximum efliciency. And this involves an appreciable element of time. Therefore, the baking time in the making of cores with this milk binder is very much less than that required in,

sand from the recesses of the casting.

finally, the sand, after use, is left in subh condition that it may be med again and again. Furthermore, in the casting of low-melting metals, where the heat is less-effective in the burning out of the binder, the advantage of the binder of this invention overv the'binders usually employed is, for the reasons stated, great.

It is customary in some foundries to use a' combination of binders, of the oil type and of the dry type together, in the making of a single core. In carefully controlled tests it has been found that my binder and an oil binder can be used together quite successfully, and that in this use the intrinsic merits of my binder are still to be enjoyed. For example, my binder may be substituted to the extent of twenty-five per cent. of the core 011 used in making a certain type of core, and a core produced as strongin transverse breaking strength as one prepared with oil alone; and at the same time the surface qualities of my core will be attained. The figure here given is given by way of example merely, andisnottobetakenasalimitationuponthe ratio of suchamix. Itwill beunderstoodthata binder including oil is necessarily subject to the delay in manufacture that is requisite to accomplish oxidation. The advantages of the invention, however, in other respects remain.

I claim as my invention:

1. A baked core for foundry use A of a body of sand with a binder of milk solids eoncentrated atthe surface, leaving the interior relatively friable.

2. A core of a mixtureof finely divided solid material and'a binder consisting of milk solids, watersoluble and susceptible, during the evaporation of the water content, to migration to the surface of the core. 1

3. A core material for foundry use consisting of a mixture of finely divided inert material.

and a binder consisting of a milk concentrate that includes the whey solids.

4. A core material for foundry use consisting of a mixture of finely divided inert material and' a binder including concentrated skim milk.

material .for use consisting 5.'A core material for foundry use consisting.

of an aqueous mixture of finely divided inert solids and milk powder; v

8. A core material for foundry useconsisting .of a mixture of finely divided material and milk. v

,7. The method herein described of preparing material for foundry use which consists in working into a plastic with water finely divided solids and milk powder.

s. The method herein described of forming a molded article which consists'in preparing a plastic of finelydivided solid material and water-soluble milk solids, shaping and applying heat to the shaped article and in so doing effectingmigration of the milk solids from deeper portions toward the surface and consequent induration of the articl the induration being pro ressive in'greater degree from the can towardthesurfaeeofthearticle. A

EDWARD WEATHIRI'ORD. 

